JP4056482B2 - Electrostatic machine and method of manufacturing the same - Google Patents

Description

  The present invention relates generally to the fabrication of mechanical structures, and more particularly to the fabrication of machines comprising multiple layers of micro-structures formed separately and then stacked in a stack arrangement selected to form the machine. Related to.

  Although micromachine technology continues to evolve rapidly, such machines have in fact generally been used only as microsensors. For example, there is a silicon microsensor chip that detects mechanical vibration and sets acceleration, and there is also a microsensor called a silicon diaphragm pressure sensor that measures pressure. Chemical sensors that detect material ion concentration, dielectric properties, organic vapor concentration, gas concentration, and the like are also fabricated on a silicon substrate.

  Most micro structures such as diaphragms and microbridges were structures with relatively immovable elements or members. Recently, however, micromachine technology has been extended to the production of microactuators having movable members. See, for example, US Pat. Nos. 4,943,750 and 4,997,521, both named “Electrostatic Micromotor”.

  Using basic silicon technology, many movable micro objects formed as machines can be fabricated on a silicon substrate. These micromachines are composed of micro structures defined on a single substrate using conventional large scale integration (LSI) or very large scale integration (VLSI) processing. Unfortunately, a significant drawback of existing micromachines is that they are not very small and have few practical applications. For example, a 1 micrometer × 0.1 micrometer electrostatic motor may not drive anything except perhaps other micromachine gears.

  Therefore, the present invention is a new extension of the existing micromachine technology that pursues the practical application of micromachine technology. It is an object of the present invention to provide a machine capable of useful work that is fabricated using micromachine technology, but much larger than that implemented with micromachine technology.

  In summary, the present invention, in a major aspect, discloses a machine that includes a stack structure formed of a plurality of stacked layers. The stack structure includes a movable member defined from a micro structure of at least one of the layers including a plurality of layers in the stack. As a specific example, the machine includes an electrostatic motor with a stack including a stator structure and a rotor structure arranged to move relative to the stator without contacting the stator. Can do. The rotor structure is defined from a micro structure of at least one micromachine layer in a plurality of layers including the stack.

  In another aspect, the invention provides providing a plurality of substrates, forming at least one hole in at least one substrate, wherein at least one hole defines a structure in at least one substrate; Filling at least a portion of at least one hole with a sacrificial material to temporarily secure selected structures separated by at least one hole, and stacking a plurality of substrates in a selected arrangement Forming a stack structure and removing a sacrificial material from at least one hole such that a structure defined in the substrate by the hole includes a movable member in the stack structure, thereby forming a machine. Includes machine fabrication methods.

  In another aspect, the holes define a micro-structure in the substrate that makes up the machine when the substrates are stacked in a selected arrangement, forming at least one hole in each of the at least two substrates. At least some of the holes in the substrate are filled with a sacrificial material to temporarily secure selected micro structures separated by holes, and the substrate in a selected arrangement Stacking and forming a stack and removing sacrificial material from holes in the substrate, wherein the movable member is defined in the stack by a stacked micro-structure of at least two substrates forming the stack; Disclosed is a method of making a machine thereby forming a machine.

  Although described herein with reference to electrostatic machines, particularly electrostatic motors, those skilled in the art will equally appreciate that the concepts presented are equally applicable to the fabrication of a wide variety of machines having one or more movable members. It will be understood that it is possible. Conceptually, the present invention uses a series of masks to define layers or slices on a substrate or wafer that are subsequently assembled in a selected arrangement to form a stack containing machines. The movable member is temporarily held in the layer by the sacrificial layer until the stack is formed. By manufacturing the machine as a stack, machines with dimensions from micrometers to millimeters and centimeters can be realized. In essence, the proposed concept makes it possible to produce a machine that is sized to fill an existing gap between a macro (centimeter) sized machine and a micro sized machine.

  In addition, a variety of machines can be constructed using the techniques presented herein. For example, each individual layer of the stack can include a different micromachine structure. Alternatively, if the same structure is included, the structures can have different sizes and / or shapes. For example, pear-shaped rotors can be conceived and constructed in a radial fashion using the stratification approach presented herein. There is almost no limit to what can be done using the basic concepts herein.

  FIGS. 1 and 2 illustrate one embodiment of a micromachine layer (generally indicated at 10) partially defined in the substrate 12. Layer 10 is defined by holes or grooves 14 in substrate 12 that are patterned using first mask 13 (shown in dotted lines). The micromachine layer includes a stator structure 16 and a rotor structure 18. In this embodiment, the mask 13 also forms a second hole 20 in the substrate that defines the hub 22. Finally, when an appropriate potential is applied to the stator structure 16 in a manner well known in the art, the rotor structure 18 rotates about the hub. Therefore, the micromachine layer 10 includes an electrostatic micromotor. The electrostatic micromotor is preferably defined using very large scale integration (VLSI) techniques. The substrate structure (16, 18, 20) defined by the holes 14 and 20 is referred to herein as an “microstructure” within the micromachine layer 10. It should also be noted that in this embodiment, only the rotor 18 constitutes a movable member in the micromachine.

  As an example, the substrate 12 can comprise a crystallographically oriented silicon substrate or silicon wafer so that holes can be formed using directional wet etching. Holes 14 and 20 are preferably time etched to pass through at least half of substrate 12. It is therefore necessary to wet etch to achieve the desired depth. Silicon wet etching is well known in the art. For example, refer to the form described in "Accelerated Etching of Silicon in Anisotropic Ethylene Diamine-Water-Pyrazine-Pyrocathecol Bath", IBM Technical Disclosure Bulletin (Vol.31, No. 7, December 1988) I want to be.

  In accordance with the present invention, sacrificial layer 24 (FIG. 3) is then conformally deposited on top surface 15 of substrate 12 such that holes 14 and 20 meet top surface 15. After filling the holes, the sacrificial layer 24 is re-planarized in any suitable manner so that the sacrificial material remains only in the holes 14 and 20. Suitable sacrificial materials include certain metals and polycrystalline materials as well as materials such as polyimide, paralyene, nitride, or oxide. The material requirement is that the selected sacrificial material must be cleanly removed in the wet bath, while the silicon substrate or the micro structure formed therein (eg, stator, rotor, hub) is etched. It must not be. Although not shown in FIG. 1, those skilled in the art are able to separate the three faces of each stator structure 16 that are not facing toward the rotor 18 from the substrate 12 via a hard non-removable insulating layer. You will understand. Obviously, this insulating layer will comprise a different material than the sacrificial material that fills the remainder of the hole.

  Next, the substrate 12 is turned over so that the lower surface of the substrate 12 is at the top, and the processes of FIGS. 1 to 3 are repeated. Specifically, a second mask 26 is formed on the upper surface 17 of the substrate 12, and a pattern is formed by the first hole 28 and the second hole 30. These holes are arranged so as to be aligned with holes or grooves that intersect the upper surface 15 already formed on the substrate 12. Infrared radiation can be used to align the holes in the second mask with holes already formed in the substrate 12. In the case of this second etching operation, the filled hole serves as an etch stop, so that the etching of the hole from the surface 17 into the substrate 12 can proceed in a non-timed manner. Next, the hole that intersects surface 17 is filled with a sacrificial material such as that used to fill the hole that intersects surface 15. As a result, filled through holes or holes 14 'and 20' will extend between the major planes 15 and 17 of the substrate or wafer. Note that the sacrificial material deposited in these holes holds the rotor, hub, and stator structure in a fixed positional relationship. If this material is removed at this point, the hub and rotor will be separated from the substrate. It should also be noted that a non-removable insulating material can be selectively used in the holes 14 'and 20', depending on the machine being built.

  Referring to FIG. 6, the same micromachine layer 10 ′ is fabricated and then stacked in a selected arrangement to form a stack structure 40. As used herein, “stack” includes a monolithic structure in which at least one major plane of each layer is stacked on the major plane of an adjacent layer. In this embodiment, the arrangement is such that the holes 14 'and 20' through each micromachine layer in the stack are aligned. Substrate or chip stacking is now well known in the art. See, for example, commonly assigned U.S. Pat. Nos. 5,202,754, 5,270,261, and 5,426,566.

  During stacking, the layer 10 'can be stacked using various techniques. For example, an adhesive can be used only on the outer edge of each layer. If the adhesive process creates a thickness that prevents the micro structure (eg, hub, rotor, stator structure) from contacting, an additional mask can be used during processing to accept the outer edge of each layer. You can also dent a sufficient amount. Alternatively, a layer such as titanium or tungsten is formed on the main plane of each substrate before forming the holes in each substrate, and the titanium or tungsten layer is self-aligned to the holes once the holes are formed, and later It is also possible to use it when placing the micromachine layer in the stack structure. When heat treatment is performed with the titanium or tungsten layer in the stack, electrical or mechanical bonding between the aligned microstructures of the various layers in the stack is enhanced.

  7 and 8 illustrate a machine 70 completed according to the present invention. The machine 70 uses the stack structure 40 of FIG. 6 and, as shown, uses an end cap micromachine layer 50 as the end layer of the machine. The end cap layer 50 is disposed at each end of the stack and functions to hold the movable member in the machine in place. Without such a cap structure, the sacrificial material is removed from the holes in the layer 10 'while at the same time the rotor structure and hub structure are easily separated from the rest of the stack. One skilled in the art will recognize that the cap 50 can be fabricated by the same or similar processes as described above for the micromachine layer 10 ', but the mask used is clearly different.

  The end cap layer 50 includes a hard insulator 56, such as a nitride, to electrically insulate the structure 54 that electrically connects to the stacked stator microstructures of the micromachine layer 10 '. A gap 60 is provided between adjacent micromachine layer 10 ′ and endcap micromachine layer 50 in the region of the rotor to allow the rotor to rotate freely without contacting the endcap layer. . In this embodiment, the fixed hub structure 58 is positioned so that the hub structure contacts the adjacent micromachine layer 10 '. However, it should be noted that the hub structure may or may not be connected to the rotor structure in the micromachine layer. When the hub structure is connected to the rotor, the configuration of the end cap layer 50 is clearly different. For example, if the hub needs to drive a mechanism external to the machine, the hub must be connected to the rotor structure and the end cap layer will be designed to drive the external shaft.

  FIG. 8 is the structure of FIG. 7 after immersion in an etchant to remove the sacrificial material from the various layers. Communication with the sacrificial material and etching of the sacrificial material will be done through access holes (not shown) in the end cap layer 50. Prior to final packaging, electrical signal lines are connected to the stator structure. Existing VLSI techniques can be used to provide a strengthening mechanism (not shown) in the basic electrostatic motor presented herein. For example, bushings, bearings, micro lubricants, timing elements, etc. can be added.

  Although described herein with reference to electrostatic machines, particularly electrostatic motors, those skilled in the art will be equally applicable to the fabrication of a wide variety of machines having one or more movable members. You will see that there is. For example, in an electrostatic machine, the layers containing the rotating members are not connected, can be made differently thin to rotate at different speeds, and can even be controlled to rotate in different directions if desired. . This can be achieved if the two rotor segments are in contact with the stator structure separately at each end of the stack and separated near the center. Furthermore, if at least one stator structure is used as a speed sensor, the speed of the rotor structure can be controlled using feedback. For example, the rotational speed can be related to a groove etched into the rotor.

  Conceptually, the present invention uses a series of masks to define layers or slices on a substrate or wafer and later assemble in a selected arrangement to form a stack, thereby forming a machine. The movable member is temporarily held in the layer by the sacrificial layer until the stack is formed. By manufacturing the machine as a stack, it is possible to realize machines with dimensions from micrometers to millimeters and centimeters. In essence, the concepts presented can produce a machine that is sized to fill an existing gap between a macro (centimeter) sized machine and a micro sized machine.

  In addition, a variety of machines can be constructed using the techniques presented herein. For example, each individual layer of the stack can include a different micromachine structure. Alternatively, if the same structure is included, the structures can have different sizes and / or shapes. For example, the stratified approach presented herein can be used to conceive and construct a radialless rotor. There is almost no limit to what can be done using the basic concepts herein.

  Although the present invention has been described in detail herein according to certain preferred embodiments of the present invention, those skilled in the art can make many modifications and variations to the present invention. Accordingly, it is intended by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the invention.

It is a top view of the electrostatic micromachine layer manufactured by this invention. 2 is a cross-sectional view of the micromachine layer of FIG. 1 taken along line AA. FIG. FIG. 3 is a cross-sectional view of the micromachine layer of FIG. 2 after sacrificial material is deposited and coplanarized in a defined hole. FIG. 4 is a cross-sectional view of the micromachine layer of FIG. 3 inverted and with the pattern mask placed in alignment with the holes already formed in the micromachine layer. FIG. 5 is a cross-sectional view of the micromachine layer of FIG. 4 after forming holes in the patterning surface and filling the holes with a sacrificial material. FIG. 6 is a partial cross-sectional view of a stack formed from a stack of multiple micromachine layers, each layer including the structure of FIG. FIG. 7 is a partial cross-sectional view of a machine made from FIG. 6 in accordance with the present invention, still with sacrificial material. FIG. 8 is a partial cross-sectional view of the machine of FIG. 7 after the sacrificial material is removed such that the machine includes a movable member defined by a plurality of micromachine layers.

Explanation of symbols

10 Micromachine layer 12 Substrate 13 Mask 14 Hole 15 Main plane (upper surface)
16 Stator structure 17 Main plane (upper surface)
18 Rotor Structure 20 Hole 22 Hub 24 Sacrificial Layer 28 Hole 30 Hole 40 Stack Structure 50 End Cap Layer 56 Insulating Material 58 Hub Structure 60 Gap 70 Machine

Claims (5)

  A stack structure including a plurality of layers formed independently and stacked in a stack, the plurality of layers of the stack structure including at least two micromachine layers, each of the micromachine layers being a hub A micro structure having the same shape including a rotor structure and a plurality of stator structures arranged adjacent to the periphery of the rotor structure, and the hubs of the plurality of micromachine layers are bonded to each other. An electrostatic machine, wherein the rotor structures of the plurality of micromachine layers are bonded to each other, and the stator structures of the plurality of micromachine layers are bonded to each other.   Two end cap layers are provided so as to sandwich the at least two micromachine layers, and each of the two end cap layers is connected to the hub and is disposed via a gap from the rotor structure. The electrostatic machine according to claim 1, comprising:   The electrostatic machine according to claim 2, wherein an electrical connection portion connected to each of the plurality of stator structures is provided on at least one of the two end cap layers.   The electrostatic machine of claim 1, wherein the rotor structure rotates about the hub. Wherein and rotor structure is connected to at least one of the hub structure of the two end caps layer via the hub, according to claim 2 wherein said hub structure and said and rotated Turkey by the rotor structure Electrostatic machine as described in.

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